Heat exchanger

ABSTRACT

A heat exchanger which is used to reheat a recirculated heating fluid in which most of the recycled fluid and most of the makeup fluid is mixed outside of the heat exchanger and fed to the heat exchanger via a bottom inlet. A small proportion of the recycled fluid and a small proportion of the makeup fluid is mixed outside of the heat exchanger and fed to an inlet at the top of the heat exchanger. This second flow of fluid passes through a control chamber mounted inside the heat exchanger to permit the temperature of this flow to be sensed by a temperature controller, which regulates the heat input to the heat exchanger.

United States Patent 2,713,994 7/1955 Angelery Inventor Henry Brants 444Sanford Ave., St. Lambert, Quebec, Canada Appl. No. 871,928 Filed Oct.28, 1969 Patented Sept. 14, 1971 Priority Dec. 18, 1968 Canada 038,193

HEAT EXCHANGER 6 Claims, 2 Drawing Figs.

US. Cl 165/1, l22/32,165/36,165/39,165/108 Int. Cl ..G05d 23/00, B60hl/00, F28f l3/06 Field of Search 165/36, 39, 108, l; 122/32 ReferencesCited UNITED STATES PATENTS Primary ExaminerWilliam F. ODea AssistantExaminerP. D. Ferguson Attorney-Fetherstonhaugh & Co.

ABSTRACT: A heat exchanger which is used to reheat a recirculatedheating fluid in which most of the recycled fluid and most of the makeupfluid is mixed outside of the heat exchanger and fed to the heatexchanger via a bottom inlet. A small proportion of the recycled fluidand a small proportion of the makeup fluid is mixed outside of the heatexchanger and fed to an inlet at the top of the heat exchanger. Thissecond flow of fluid passes through a control chamber mounted inside theheat exchanger to permit the temperature of this flow to be sensed by atemperature controller, which regulates the heat input to the heatexchanger,

HEAT EXCHANGER The present invention relates to heat exchangers and inparticular to heat exchangers having improved temperaturesensingproperties.

Domestic hot water distribution systems which are used in largecommercial and industrial buildings are usually of the recycling type.In other words the hot water is taken from a storage tank and recycledthroughout the building and returned to the tank. This is done so thatthe water in the hot water pipe throughout the building is at alltimeshot, thus, whenever some person opens a faucet the time lag beforehot water actually reaches the faucet is kept to a minimum.

This hot water is normally heated in an out of contact heat exchanger inwhich the water is contained in the shell for distribution throughoutthe building and the heating medium such as steam is contained in coilsor tubes within the shell or receiver. The demand for hot water ofcourse varies greatly throughout the day and as the demand varies it isdesirable to vary the amount of heat being given off by the heatingcoils, and, since the heating coils are normally heated by steam it isthus necessary that the amount of steam being fed to the coils be variedto suit the demand of hot water.

In many systems the receiver or heat exchanger actually acts as areservoir to help reduce fluctuations in the demand and also to increasethe time in which the water is actually in contact with the heatingcoils. in such a system there is however a serious fault. When thedemand for hot water is suddenly increased there is a lag in the steamflow to the heating coils to give an increase in the heat given off bythe heating coils. To overcome this problem the heating coils in manycases are greatly increased in size so that they can produce a lot ofheat in a short period of time. This however produces another fault inthat at very low flows, the amount of heat being given off by theheating coils can greatly exceed that which is required and can resultin overheating of the water which of course is a very dangerousproposition.

One attempt to overcome this problem is discussed in Canadian Pat. No.525,474 ANGELERY which issued on May 29, 1956. In this patent there isshown a hot water receiver in which the inlet tube is a vertical pipeextending some distance into the receiver. This inlet tube contains arestriction which produces a zone of reduced pressure when there is flowin the tube. A second vertical conduit is provided which is spaced fromthe inlet tube. This conduit is open at the top to permit an inflow ofwater from the receiver. The conduit is connected at its lower end tothe inlet tube at a point downstream of the restriction. A bypass isalso provided to permit the flow of water from the inlet tube upstreamof the restriction to the conduit. A thermostat or other temperaturesensing device is located in this conduit to detect the temperature ofthe water flowing through the conduit.

In operation it will be seen that the flow of cold water through theinlet tube causes a zone of reduced pressure downstream of therestriction which induces a flow of water through the conduit. Thiswaterflowing through the conduit is a mixture of hot water from thereceiver entering the conduit at its upper end and cold water reachingthe conduit by the bypass. The thermostat located in the conduit detectsthe temperature of the flows and operates valves to control the flow ofsteam to the heating coils.

It has been found in practice that heat exchangers of the abovediscussed type have certain inherent disadvantages. Firstly, the flow ofmixed hot and cold water and the proportions of each which flow past thethermostat are determined by the design of the unit. This involves thesize and shape of restriction in the inlet tube, the design of thebypass, the form of the conduit etc. and it is extremely difficult todetermine these dimensions for a range of flows. In addition, inoperation the restriction and certain of the pipes may become fouled orpartially plugged and this can not readily be detected. Anotherdisadvantage is that in order to rectify such aproblem the wholeexchanger must be dismantled.

exchanger and the proportions of the two flows can easily be, varied tosuit the requirements of the heat exchanger. In addition the criticalparts of the heat exchanger, being the thermostat and the housing aboutthe thermostat, are adapted to be I easily removed from the heatexchanger without further dismantling of the heat exchanger so thatmaintenance can be done as simply and quickly as possible.

The present invention therefore provides in a fluid heating system inwhich the heated fluid is piped away from the heat exchanger and isreturned to the heat exchanger to be reheated and any heated fluid whichis not returned is compensated for by a cold fluid makeup, theimprovement which comprises combining most of the recycled fluid and themakeup fluid in a first conduit exteriorly of the heat exchanger andfeeding them to the heat exchanger through a bottom inlet, combiningsome small proportion of said recycled fluid and some small proportionof said makeup fluid in a second conduit exteriorly of the heatexchanger and feeding them to an inlet at the top of the heat exchanger.Said second flow comprising the small proportion of recycled fluid andmakeup fluid is then caused to flow through a control chamber within theheat exchanger such that the temperature of the second flow is sensed bytemperature responsive means which is adapted to regulate the heat tothe heat exchanger.

In addition the present invention also provides a heat exchangercomprising:

a shell;

a plurality of heating coils within said shell;

an inlet at the bottom of the shell adapted to permit passage of most ofthe fluid entering the shell;

an outlet at the top of the shell;

a second inlet at the top of the shell adapted to permit passage of asmall proportion of the fluid entering the shell, said second inletbeing provided with a perforated control chamber located within saidshell;

a temperature responsive means located within said control chamber suchthat fluid entering the shell through said second inlet is dischargedthrough said control chamber and around said temperature responsivemeans;

said temperature responsive means being adapted to regulate the heatingeffect of said heating coil.

The following is a description by way of example of a certain embodimentof the present invention, reference being had to the accompanyingdrawings in which:

FIG. 1 is a sectional side elevation of a preferred embodiment of theheat exchanger;

FIG. 2 is a schematic view showing a typical piping arrangement.

Referring to FIG. 1, the heat exchanger illustrated comprises a shellwhich is formed of an upper section II and a lower section 12 which arejoined by flanges l3 and 14 and bolts 15. The shell is supported in avertical position by legs 16.

Three bands of heating coils 17 are shown in FIG. 1. Each bank iscomposed of four spiral tubular coil members 18 which are connected atthe top to an inlet header l9 and after making six turns downwardly areconnected to an outlet header 20. The inlet header 19 and the outletheader 20 protrude through the shell and terminate in pipe connections21 and 22. The connections joining the spiral coils and the headers canbe of a permanent nature and the only screw type dismantleableconnections are on the exterior of the shell. Thus the possibility ofhaving a leaking connection in the heating coils and the possibility ofcontaminating the fluid to be heated by the heating medium is kept to aminimum.

The number of bands of heating coils, the number of coils, and thedesign of the individual coils can of course be varied to suit theindividual requirements.

The liquid to be heated enters by inlet 23 in the bottom of the shell.The inlet may be equipped with diffuser 24 to assist in distributing thecold liquid about the interior of the heat the heated fluid is pipedaway from a exchanger. The heated liquid leaves by outlet 25 at the topof the heat exchanger.

A second inlet coupling 26 is provided at the top of the heat exchangerand a small proportion of the liquid to be heated is admitted to theexchanger through this inlet whereas the greater proportion is admittedthrough inlet 23 at the bottom of the exchanger. A control chamber 27passes through the second inlet coupling 26 and extends into the shellof the heat exchanger. That part of the control chamber which is insidethe shell is perforated with a plurality of holes 28. A temperatureresponsive device 29 is located inside the control chamber 27 with theconnecting wires 30 extending upwardly through the inside of the controlchamber and passing from the top of the chamber through connection 31.

FIG. 2 illustrates the piping arrangement when the heat exchanger of thepresent invention is used with a domestic hot water heating system whichoperates on a recirculating principle ln most large buildingsarecirculating system is used in conjunction with the domestic hot waterpiping layout. In such a system the hot water is taken from the heatexchanger pumped throughout the building and returned to the heatexchanger for reheating. The hot water leaves the heat exchanger by apipe 43 and returns to the heat exchanger in return pipe 32. This returnflow is divided into two streams, pipe 33 being used to direct most ofthe return flow to inlet coupling 23 at the bottom of the heat exchangerand a minor portion of the return flow is directed along pipe 34 toinlet coupling 26.

All of the circulated hot water which is used up must be replaced byfresh, cold water. This fresh water makeup is added by pipe 35 which inturn is divided to provide a main flow along pipe 37 to join up withreturn pipe 33 at Tee 38 to enter the heat exchanger by coupling 23. Asmall proportion of the fresh water makeup is directed along pipe 39 tojoin return pipe 34 at Tee 40 and enter the heat exchanger by topcoupling 26. The proportions of return water and cold makeup waterentering the heat exchanger via top coupling 26 may be varied by valves41 and 42. The water entering the heat exchanger by coupling 26 flowsdown through the control chamber 27 and contacts the temperatureresponsive device 29 which in turn controls valve 45 in the steam line44 feeding the heating coils 17. The temperature-responsive device isthus contacted by a flow of fluid entering the heat exchanger which is asampling of the main flow entering the bottom of the exchanger throughcoupling 23 and diffuser 24. The temperature-responsive device can thussense a future change in temperature of the fluid in the body of theheat exchanger and immediately regulate the steam flow accordingly. Whenthere is no flow of fluid into or out of the heat exchanger the holes 28in the control chamber 27 permit the fluid in the heat exchanger tocirculate about the temperature responsive device 29 so that any smallchanges in temperature may be detected and corrected.

The mixing of the return water and the makeup water is accomplishedexteriorly of the heat exchanger and the ratio of return to makeup maybe varied to give optimum results by simply changing the setting ofvalves 41 and 42. This is a great improvement over prior art deviceswhich usually cannot be varied by the operator and may actually changedue to scaling or fouling.

The proportion of water which is fed through the top inlet 26 ascompared to the flow of water through the bottom inlet 23 does notappear to be critical. Substantially less than percent flow through thetop inlet 26 and thus through the control chamber has given excellentresults.

Another feature of the present invention is that the whole controlchamber and temperature responsive device may be adapted to be removedcompletely from the heat exchanger thus greatly reducing maintenanceproblems.

What i claim is:

1. In a method of operating a fluid-heating system in which heatexchanger and is returned to the heat exchanger to be reheated and anyheated fluid which is not returned is compensated for by a cold fluidmakeup, the improvement which comprises combining most of the recycledfluid and the makeup fluid in a first conduit exteriorly of the heatexchanger and feeding them to the heat exchanger through a bottom inlet,combining some small proportion of said recycled fluid and some smallproportion of said makeup fluid in a second conduit exteriorly of theheat exchanger and feeding them to an inlet at the top of the heatexchanger, the relative proportions of recycled fluid and makeup fluidintroduced into said second conduit being adjustable to alter thetemperature characteristics of the second conduit flow relative to thoseof the first conduit flow, causing said second flow comprising the smallproportions of recycled fluid and makeup fluid to flow through a controlchamber within said heat exchanger such that the temperature of saidsecond flow is sensed by a temperature responsive means which is adaptedto regulate the heat to the heat exchanger.

2. The method of operating a heating system as claimed in claim 1 inwhich when there is no flow of recycled fluid and makeup fluid throughthe inlet at the top of the heat exchanger, the fluid in the body of theheat exchanger circulates through said control chamber and about saidtemperature responsive means.

3. The method of operating a heating system as claimed in claim 1 inwhich the volume of flow through said inlet at the top of the heatexchanger is less than 10 percent of the volume of flow through theinlet at the bottom of the heat exchanger.

4. The method of operating a heating system as claimed in claim 3 inwhich the proportion of flow through said inlet at the top of the heatexchanger and said inlet at the bottom of the heat exchanger isvariable.

5. A heat exchanger comprising:

a shell;

a plurality of heating coils within the shell;

a first inlet at the bottom of the shell;

a second inlet at the top of the shell;

an outlet at the top of the shell;

a control chamber inside said shell adjacent said second inlet andadapted to receive fluid admitted into said shell therethrough;

temperature control means located within said control chamber responsiveto the temperature of fluid admitted thereinto from said second inlet toregulate the heating effecting of said heating coils;

first conduit means for discharging heated liquid from said outlet atthe top of said shell;

second conduit means for introducing recycled heated liquid into saidfirst inlet at the bottom of said shell;

third conduit means for introducing cold makeup fluid into said secondconduit means upstream of said first inlet whereby a mixture of recycledfluid and makeup fluid may be introduced into said shell through saidfirst inlet;

fourth conduit means for conveying a portion of recycled fluid from saidsecond conduit means to said second inlet at the top of said shellwhereby a portion of the recycled heated liquid is introduced into saidshell through said second inlet;

fifth conduit means for conveying a portion of said cold makeup fluidfrom said third conduit means to said fourth conduit means upstream ofsaid second inlet whereby a mixture of recycled fluid and makeup fluidmay be introduced into said shell through said second inlet;

first valve means in said fourth conduit for regulating the flow ofrecycled fluid therein relative to the flow thereof in said secondconduit; and

second valve means in said fifth conduit for regulating the flow ofmakeup fluid therein relative to the flow thereof in said third conduit;

said first and second valve means together regulating the amount offluid entering the shell through the second inlet relative to thatentering the bottom inlet and regulating the ratio of makeup fluidrelative to recycled fluid entering the shell through said second inletindependently to said ratio entering the shell through said first inlet.

6. The heat exchanger as claimed in claim 5 in which the walls of saidcontrol chamber are perforated to permit the fluid in the shell of theheat exchanger to circulate about the

1. In a method of operating a fluid-heating system in which the heatedfluid is piped away from a heat exchanger and is returned to the heatexchanger to be reheated and any heated fluid which is not returned iscompensated for by a cold fluid makeup, the improvement which comprisescombining most of the recycled fluid and the makeup fluid in a firstconduit exteriorly of the heat exchanger and feeding them to the heatexchanger through a bottom inlet, combining some small proportion ofsaid recycled fluid and some small proportion of said makeup fluid in asecond conduit exteriorly of the heat exchanger and feeding them to aninlet at the top of the heat exchanger, the relative proportions ofrecycled fluid and makeup fluid introduced into said second conduitbeing adjustable to alter the temperature characteristics of the secondconduit flow relative to those of the first conduit flow, causing saidsecond flow comprising the small proportions of recycled fluid andmakeup fluid to flow through a control chamber within said heatexchanger such that the temperature of said second flow is sensed by atemperature responsive means which is adapted to regulate the heat tothe heat exchanger.
 2. The method of operating a heating system asclaimed in claim 1 in which when there is no flow of recycled fluid andmakeup fluid through the inlet at the top of the heat exchanger, thefluid in the body of the heat exchanger circulates through said controlchamber and about said temperature responsive means.
 3. The method ofoperating a heating system as claimed in claim 1 in which the volume offlow through said inlet at the top of the heat exchanger is less than 10percent of the volume of flow through the inlet at the bottom of theheat exchanger.
 4. The method of operating a heating system as claimedin claim 3 in which the proportion of flow through said inlet at the topof the heat exchanger and said inlet at the bottom of the heat exchangeris variable.
 5. A heat exchanger comprising: a shell; a plurality ofheating coils within the shell; a first inlet at the bottom of theshell; a second inlet at the top of the shell; an outlet at the top ofthe shell; a control chamber inside said shell adjacent said secondinlet and adapted to receive fluid admitted into said shelltherethrough; temperature control means located within said controlchamber responsive to the temperature of fluid admitted thereinto fromsaid second inlet to regulate the heating effecting of said heatingcoIls; first conduit means for discharging heated liquid from saidoutlet at the top of said shell; second conduit means for introducingrecycled heated liquid into said first inlet at the bottom of saidshell; third conduit means for introducing cold makeup fluid into saidsecond conduit means upstream of said first inlet whereby a mixture ofrecycled fluid and makeup fluid may be introduced into said shellthrough said first inlet; fourth conduit means for conveying a portionof recycled fluid from said second conduit means to said second inlet atthe top of said shell whereby a portion of the recycled heated liquid isintroduced into said shell through said second inlet; fifth conduitmeans for conveying a portion of said cold makeup fluid from said thirdconduit means to said fourth conduit means upstream of said second inletwhereby a mixture of recycled fluid and makeup fluid may be introducedinto said shell through said second inlet; first valve means in saidfourth conduit for regulating the flow of recycled fluid thereinrelative to the flow thereof in said second conduit; and second valvemeans in said fifth conduit for regulating the flow of makeup fluidtherein relative to the flow thereof in said third conduit; said firstand second valve means together regulating the amount of fluid enteringthe shell through the second inlet relative to that entering the bottominlet and regulating the ratio of makeup fluid relative to recycledfluid entering the shell through said second inlet independently to saidratio entering the shell through said first inlet.
 6. The heat exchangeras claimed in claim 5 in which the walls of said control chamber areperforated to permit the fluid in the shell of the heat exchanger tocirculate about the temperature responsive means, when there is no flowof recycled fluid and makeup fluid through said inlet at the top of theheat exchanger.